Power units are often operated for brief periods or intermittently at very high power, in particular in applications such as servo drives, soft starters, cranes or lifting devices, as well as welding devices. There is therefore a need for heat sinks that reliably protect the semiconductors from overheating, even during peak loads. Adequate heat dissipation is essential during intermittent operation, since not only must the maximum junction temperature not be exceeded, but care must also be taken, for reasons relating to the service life, that the temperature does not vary excessively.
In the past, semiconductors and other electrical components, such as power resistors or the like, have been assembled on substrates that are both electrically insulating and good heat conductors, such as a direct bonded copper (DBC) or insulated metal substrate (IMS). When discrete, non-insulating components are used, the electrical contact is conventionally produced by soldering into a circuit board, and the thermal coupling, which is required in order to dissipate the heat, is produced by pressing the substrate against a heat sink. The electrical insulation between the component and the heat sink is eliminated by foils which conduct heat but not electricity.
This technique has the drawback, however, that foils of this type, on the one hand, are relatively expensive and, on the other hand, entail an additional assembly step.
DE 102 50 604.3 discloses an integrated circuit system comprising a latent heat storage unit, wherein, in order to improve heat dissipation, the power electronic modules are assembled directly on heat sink elements, which, on the one hand, dissipate the heat into a latent heat storage medium and, on the other hand, provide electrical contact.
Although this solution allows complicated electrical insulation between the heat sink and the power electronic modules to be dispensed with, it has the serious drawback that, because of the absence of a substrate that is compatible with standard procedures, both the overall structure and the assembly technique are comparatively problematic.